Based on the quantity of acid present in a battery, lead-acid batteries are classified as either flooded or starved electrolyte batteries. In flooded batteries, acid is in excess which is also referred to as free acid. Whereas, in starved electrolyte batteries there is no excess or free acid. Starved batteries are designed such that all the acid in the battery is immobilized in the plates and in either the separators or in gel form. Where the acid is immobilized in the separators, the battery is referred to as an absorbed glass matrix (AGM) battery. Where the acid is immobilized in the gel form, the battery is referred to as a gel type battery.
A valve regulated lead-acid (VRLA) battery is a starved electrolyte AGM type battery and has a safety valve which prevents excessive build up of gas pressure inside the battery. A key for the successful operation of a VRLA battery is the oxygen recombination reaction which prevents the water loss from a battery by recombining the oxygen and by suppressing hydrogen gas liberation at the negative electrode. The starved acid design of the battery facilitates the oxygen recombination reaction. The recombination reactions are facilitated by the starved acid or electrolyte condition where the electrolyte is immobilized in glass separators disposed between the plates of the battery.
VRLA batteries have numerous advantages over their counterpart flooded batteries, such as, for example, low maintenance, ease of handling, and high power density. However, deficiencies in VRLA batteries include: a) recombination reactions tend to generate excessive heat and accelerate thermal runaway processes; b) under uncontrolled environments, VRLA batteries dry out since the batteries have a limited amount of electrolyte; c) low heat dissipation; and d) self discharge of the negative electrode leads to premature capacity loss and battery failure. These deficiencies are unique to VRLA batteries.
A need has thus arisen for an improved VRLA battery designed for longer life.